For example, an imaging device comprising a polarizing filter, a retroreflective prism, and a retardation film has been proposed. With this imaging device, an aerial image representing a display image is formed at a plane-symmetrical position of an emission point of display light representing the display image with respect to the polarizing filter.
Further, an imaging optical system structured by combining a screen-cum-half mirror and a retroreflector array has been proposed. With this imaging optical system, an image projected from a projection optical system and an aerial image representing the image of an object to be observed are observed.
In various display devices as described above, in an off-state in which the aerial image is not displayed, the internal structures are visually recognized, and thus, improvement of the appearance has been desired.